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May 30, 2013

The Schürzen - against HEAT?

SS: This is a translation of Tuccy's post on Schürzen. For those who don't know him, Tuccy is a Czech community organizer and a tank buff - in fact, he's one of the most knowledgeable people on any WoT forums, when it comes to real life tanks and history - compared to him, I'm a schoolkid. So when he writes something, it's really worth reading. This time, he wrote about the Schürzen and the widespread myth that they were supposed to protect vehicles against HEAT projectiles.It's basically the same thing that H.Doyle said in Operation Think Tank.

Spaced armor in the form of thin metal plates, so called Schürzen ("skirts") appeared en masse around 1943 and it was immediately misunderstood. Due to the fact it came by the time the Allies discarded their AT rifles and started using hand-held HEAT warhead weapons (PIAT, Bazooka), the western authors have the tendency (supported by copying each other's texts) to state that this was to protect the tanks from HEAT warheads.

Luckily for us, we have our well-informed original sources, that give us proper insight - in form of German documents (for example in Spielberger's books on Panzer III, Panzer IV and Panther). During the Schürzen development, following threats were considered:

- 14,5mm shots from Soviet PTRS and PTRD anti-tank rifles
- HE shells from field gunsRegarding the AT rifles:

June 1941 caught the Red Army off-guard and without proper anti-tank armament. One of the weapons designed to rectify this situations were simple, mass-produced 14,5mm rifles. Compared to their German counterparts, their caliber was bigger (SS: Germans used 7,92mm special long cartridges) and compared to their western allied counterparts, they were often lighter and balistically more powerful - essentially, it was the peak of AT rifle development, beause - unlike early rocked or recoilless guns with HEAT warheads, they were reliable and (what was even more important) they didn't require new industrial capacities.

Their penetration ability (at least 35-40mm at 100m) was fully sufficient to penetrate Panzer III, IV and Panther side armor and proved to be a serious threat also to lightly-armored tank destroyers and self-propelled anti-tank guns. Furthermore, they were used en-masse, a Soviet batallion anti-tank company consisted usually of one platoon with 45mm guns and two or three platoons with 8 AT rifles each. Regarding the HE shells:

Lack of arms and ammunition in June 1941 led to massive use of HE shells against tanks (in Fall 1941, there were only 10 76,2mm AP shells per barrel on average in the Red Army, they were also BR-350 and BR-350A shells of dubious quality). HE shells fired from field guns (75-76mm) could eventually penetrate up to 30mm of armor and even if they didn't penetrate it, they at least caused spalling.

Since it would be too expensive and complicated to rebuild the tanks, that were destined to be replaced soon anyway (Panzer III, IV), the German engineers accepted the relatively simple Schürzen solution despite the fact that it brought increased weight with it. What was even more annoying that the relatively thin vertical side armor strip of the Panther was also vulnerable to AT rifle fire. First reaction was to initiate the Panther II development - its thicker side armor was designed to counter specifically this threat, but after the success of the Schürzen, the Panther was "saved" by having the skirts mounted on it.

This doenst mean it couldnt reduce the effectiveness of an HEAT or neutralise it completly, this just means schurzen was introduced to neutralize AT rifles and HE damage.. but it could obviously defeat HEAT.

Its true Schürzen was not developed as a defence against Shaped Charges (HEAT in this case] but it did have that added benefit, to say otherwise would be a miss truth. It was found that by detonating the HEAT round further from the primary armour surface that Schürzen fortuitously gave the jet formed by the HEAT round, room to disperse and hence reduce penetration.

If one believes Schürzen not to be effective then perhaps one can explain why the British Army insisted on fitting ‘Bazooka Plates’ to all its post war MBT’s? Spend enough time in my Army carrier taking the Bloody things off and putting them back on, to realise they sure as hell aren’t there for decoration!

Defeating heat was not just a byproduct of the Schürzen, the Germans realized that even wire mesh would set off the heat round prematurely. See Pz IV J with wire mesh "side shields".

The Germans introduced Zimmermit to combat the magnetic mines that they themselves were about to employ on the Russian front. Thus they were proactive to defending against weapons they were about to employ. Side shields/Schürzen would also be an effective counter this weapon.

Britain was the first to utilize the HEAT method of armor piercing shells in their rifle grenade.

The No. 68 was an early form of shaped charge grenade, and has some claim to have been the first High Explosive, Anti Tank (HEAT) device in use. The design of the warhead was simple and was capable of penetrating 52mm (2 inches) of armour in 1940.[1]

Thus the Germans were aware of HEAT weapons and how spaced armor would be effective, now if it was an active awareness or just a happenstance when they added the shields....

What was the timeline of the recoiless Panzerfaust development in relation to the capture of the Bazooka in N Africa and both on the introduction of the Schürzen/sideshields? Were the Germans being proactive?

Yes, I agree on the premise/exposition of defending against the anti-tank rifle...hard to hit a track you cannot even see.

The main problem that players don't recognize is difference between low velocity hand-held infantry AT-weapons working on HEAT principle (like bazooka or piat) and higher velocity HEAT shells used in tank/infantry guns.

Is there a significant difference? The fact, that side skirts provided some protection against HE shells, suggests they should provide some protection from at least infantry gun fired HEAT shells, if not from tank gun.

How does any stand off armor work? Regardless whether we are talking about Schurzen, Bazooka Plates or Slat armor currently in use. The main effect is that you initiate the fuse in some distance from the actual armor.

Fact that the side skirts provided protection against HE shells means, that even the thin, mild steel plate was able to initiate the fuse of the HE shell and cause premature detonation. As the HEAT shells are more or less the same in terms of velocity and weight as the HE shells (their kinetic penetration capability of such thin "armor" would be similar), the question is, whether the skirts were enough to initiate the fuse of the HEAT shell. I do not have any data to say yes or no, but in my opinion the answer is yes (the HEAT fuse has to be relatively sensitive, in order to assure proper and timely initiation).

As others have said, that they were not developed against HEAT does not mean they were not useful against HEAT. Similar armor is used even today to defend against HEAT warheads.http://defense-update.com/wp-content/uploads/2012/06/leo2a6can_rpg.jpg

A lot of tanks were outfitted with spaced armor as well to defend against HEAT shells before composite armor came around for MBTs. See later versions of the Leopard 1 for example, which had spaced armor added at least to the turret.As long as the Schürzen would detonate a HEAT warhead early, they should offer additional protection. It's not like the HEAT warhead asks what the inventor of the Schürzen had in mind, or is it? ;)

hmm yes and now. Maybe today there is an effect with this massive bars. But in WW2 Schürzen almost didnt affect HEAT shells at all. The german WaPrü Amt tested it in 1944 with german Panzerschrecks and -fäusten and wiremesh and 5mm steel sheet Schürzen were almost total useless.

You're right, my fault.I forgot what the tank expert in that expert interview said. Basically the HEAT stream is more effective at a distance and so making it explode earlier could actually help it penetrate. Modern HEAT munitions usually already explode at a distance anyway (they have long tips/"noses") so I guess the standoff distance helps more there because in that case they do not explode at the optimal distance anymore.

So it's not so much about the spaced armor itself but about the actual relation between the distance between the actual armor and the standoff armor and the optimal distance between the armor and the explosion of the shell. Since the first HEAT shells did usually not explode at the optimal distance at which the hot stream can form optimally, the standoff armor could help them do just that.

Maybe include that in the original text since the reasoning there was still weird IMO.

Another thing that is commonly missed is that the Soviet troops commonly used magnetic grenades (reason for cheramic coating on mid war German tanks) the Schützen was also protecting the tanks versus this threat.

Velocity of the shaped charges has very low impact on penetration properties, an example of this is when German paratroopers used shaped charges to defeat the Belgian fort Eben-Emael. The sharges used looked a lot like tin cans on legs.

Very unlikley.Just a quote frome the20. Pz. Div. It is in german sorry.It basically says, an huge disadvantage of the schürzen is, that explosives thrown on a tank could not fall of the tank. In the worst case in fall between the tank and the Schürzen and the explosion will be strengthened.

No they didn't. No Soviet magnetic grenades. Zimmeritt is more camouflage than naything else-yet another war myth about magnetic bs. The Germans weren't stupid enough to waste huge amounts of time and money to proect against a non-existent enemy wewapon.

The Wehrmacht was aware that the Schürzen offered protection against HEAT warheads. That was in fact one of the main problems during the development of the Panzer-Wurfkanonen as they fired HEAT rounds exclusively. The PWK 8 H 63 with a normal penetration of 140mm@60° failed to penetrate 40 or 60mm armor plates protected by 10mm Schürzen in about 75% of the tests.

Schurtzen and other improvised armor (sand bags on the shermans are a well known example here) can actually serve to increase the penetration potential of HEAT shells.

HEAT shells have to form their metal "jets" and need a certain standoff distance for that. Back in those days, detonators were not yet well capable of detonating at the optimal distance, but closer. So armor add-ons that increase the distance to the main armor actually helped the HEAT shell penetrate it.

Another little known fact: HEAT shells do not "melt" through the target with the copper (or sometimes iron or even glass) jet. While the copper may melt (or more accurately: liquified) during the detonation, it is the kinetic energy of the jet that punches through the armor in the exact same way any other AP (APBC, APCR, APFSDS, etc) shell does. The shell itself is much like a gun that is carried to the target to shoot it at point-blank range (and thus not lose penetration over long range). The jet can reach velocities several times those of regular AP shells and even greatly exceed that of the modern APFSDS rounds by roughly 50%, while the very small diameter of a well-engineered HEAT shell's copper jet increases local pressure on the armor even further. Thermal effects are negligible.

To get back to the subject of optimal standoff distance, this is greatly influenced by the shape of the copper liner of the shell. A long cone shape will have a very short standoff optimum, while a flatter, pancake-like shape can have an optimal standoff of several dozen meters. In this case, they are generally referred to as EFPs, or Explosively Formed Penetrators, and they are the type often used both in IEDs as well as modern anti-tank missiles that attack the target top-down during horizontal flight (unlike the Javelin for example, which engages in a dive).

HEAT does not work by thermal energy, it works by KE of super-fluid copper jet. Copper is not even molten in HEAT jet, temperature is less then melting point of copper (melting it would actually fuck up efficiency of HEAT).

Armor-HEAT jet interaction is best described as high pressure water hose hitting sand.

Modern slat armor works in different way that providing stand off, works by crushing RPG-7 front cone and short-fusing it while damaging rear HEAT coneand making it less effective in case it fuses anyway. (look on PG-7V cut-out to understand it), and much less useful vs other hand-held weapons that don't have same way of piezo fusing as RPG-7 (but RPG-7 is common enough to make it worth it).

*Optimal fusing distance for WW2 era HEAT was ~2 diameters of HEAT cone, so ~ 200mm for Panzerfaust, 170mm for Panzerschreck, 120mm for Bazooka. Everything over that penetration fell off rapidly until it fell to about 1/2 optimal penetrations, than fell off very gradually.Due the fusing issues, all of above did not have optimal stand-off, setting at about one cone diameter, so slight increase in stand-off (60-100mm) would benefit them. Now, that is way less then shurtsen. Lets see what happens when Bazooka hits shurtsen (~500mm stand off IIRC):first 50mm increase efficiency of Bazooka about 10%, so penetration increases to ~110mm from ~100mm.Next 4 cone diameters (200-250mm) will halve penetration to about 55mm. Next 8 CDs will only halve penetration by about 10%. So, even after shurtsen Bazooka would penetrate at least 45-50mm of armor, which Pz-III or IV side would not protect against. Also since jet is now less focused it will make larger entry hole with all bad things that came from it (eg. more spalling).Now, take PzF with it's 200mm pen in otimal circumstances and shurtsen is worth practically nothing.

Standoff distance on the schurtzen is not the same on the entire surface. Some armor will be closer behind it (upper hull) than other armor (lower hull, behind the tracks).

Also another interesting fact:High velocity guns couldn't fire HEAT because the velocity of the shell would decrease the standoff even further due to the slow fuses. In AT shells with explosive charge that was fine because it needed time to penetrate before exploding, but HEAT performance would have been abysmal. Rifled guns also aren't optimal for HEAT as the rotation of the shell helps disperse the copper jet.

Bojan, you clearly don't understand what thermal energy is :) and what's the difference between heat and temperature.Unfortunately internet is full of "experts" repeating one after another and comments under this blog post are best example :( ...

Anon1 - 1. I took best case for shurtsen stand-off and it still would not cope even with something anemic as Bazooka.2.Rifled guns fire high-velocity (velocity comparable to AP) HEAT since late '40s. By mid-50s everyone had it.

Anon2 - nothing about thermal energy is relevant for HEAT penetration. It is pure mechanical phenomenon, only thermal energy is waste heat made by penetrating jet (which is quite a lot, hence popular opinion that jet "melts" armor). Even ignition of ammo by HEAT jet is not due the jet temperature (else fuel tanks would not be used by everyone for boosting HEAT protection), but by high-speed impact into propellant which is enough to start propellant deflagration.